Many microfabrication methods involve electroplating layers of materials onto a plating template. According to some methods, the electroplated layers remain an integral part of the substrate in the finished product. However, for certain applications, for example, when it is desirable to reuse the template, or when integration with the template makes the finished product unsuitable for its intended use, it is desirable to remove the electroplated structure(s) from the template.
One current method involves undercutting the structure by removal of a sacrificial material layer similar to the way in which photolithographic lift-off layers are used in semiconductor processing techniques. However, when the lateral distance between areas directly exposed to the removal chemical (such as two intrusions to the base material) is substantial and the thickness of the release layer minimal, the release may be ineffective or take a disadvantageously long period of time. In addition, the chemicals used to effect the release (i.e. etch away the sacrificial layer) may adversely affect the desired resultant structure. Selective etches must be carefully chosen, and selectivity occurs in a matter of degrees, usually not just 100% or 0%.
Moreover, stress on the electroplated material during the removal process, or stress in the material as it is formed (which becomes apparent after the material is freed from it's binding support) can cause the electroplated layers to curl or otherwise alter or change in shape, possibly destroying the finished product(s). Methods to achieve plating of multiple metals include controlling stress by varying the plating bath chemistry/composition and by varying the electroplating current.
It is known to use an electrically conductive material (i.e. solder) to form an encompassing mass, which is then used to join two preformed parts together. The solder must initially be heated to its melting temperature before it can be used to join the preformed parts. Once the two parts are joined, the solder can be heated to release the two parts from each other. However, because one is dealing with a heated, amorphous, material that solidifies upon cooling, it is difficult to precisely control the shape or pattern the solder takes when the preformed parts are joined. Although one may produce a shaped column, using surface tension, from solder melted between two separated, already previously formed wettable areas (as in solder bump technology), this is an imprecise structure. A column formed in this manner does not have the top surface exposed and available for insitu formation of another shaped layer and can only accommodate a preformed part. Moreover, one must destroy the shaped solder to remove the preformed part.
Accordingly, it would be desirable to provide a mechanism for forming precise layers of materials (e.g. by electroplating) and selectively releasing some of the layers without imparting significant stress on the layers that are released. Furthermore, it would be desirable to provide a release layer which can impart specific, desired, structural characteristics to layers formed over the release layer.